Technology Trends

It’s not the first time that physicists claim that the speed of light can be modified, and even exceed the theoretical limit called c without violating Einstein’s laws of relativity (check for example this article from two years ago). Now, researchers from the Ecole Polytechnique Fédérale de Lausanne (EPFL) in Lausanne, Switzerland, claim that light can travel faster than light!. They were able to control the speed of light in an off-the-shelf optical fiber. They said that they did “slow a light signal down by a factor of 3.6 (or about 71,000 km/s), creating a sort of temporary “optical memory.” On the other hand, they also did create “extreme conditions in which the light signal travelled faster than 300 million meters a second.” As they don’t give any numbers for this upper limit, you have to trust them. Anyway, these results are important because they were achieved using off-the-shelf optical fibers, opening the way for future super fast all-optical routers. Update (August 22, 2005): Luc Thévenaz sent me insightful comments about this post. You’ll find them at the end of this entry.

So what have done Luc Thévenaz and his fellow researchers in the EPFL’s Nanophotonics and Metrology laboratory (page in French)?

The telecommunications industry transmits vast quantities of data via fiber optics. Light signals race down the information superhighway at about 186,000 miles per second. But information cannot be processed at this speed, because with current technology light signals cannot be stored, routed or processed without first being transformed into electrical signals, which work much more slowly. If the light signal could be controlled by light, it would be possible to route and process optical data without the costly electrical conversion, opening up the possibility of processing information at the speed of light.

This is exactly what the EPFL team has demonstrated. Using their Stimulated Brillouin Scattering (SBS) method, the group was able to slow a light signal down by a factor of 3.6, creating a sort of temporary”optical memory.” They were also able to create extreme conditions in which the light signal travelled faster than 300 million meters a second. And even though this seems to violate all sorts of cherished physical assumptions, Einstein needn’t move over – relativity isn’t called into question, because only a portion of the signal is affected.

Anyway, the real value of this research doesn’t come from light travelling faster than c, but from light travelling slower.

Slowing down light is considered to be a critical step in our ability to process information optically. The US Defense Advanced Research Projects Agency (DARPA) considers it so important that it has been funnelling millions of dollars into projects such as”Applications of Slow Light in Optical Fibers” and research on all-optical routers. To succeed commercially, a device that slows down light must be able to work across a range of wavelengths, be capable of working at high bit-rates and be reasonably compact and inexpensive.

The EPFL team has brought applications of slow light an important step closer to this reality. And Thévenaz points out that this technology could take us far beyond just improving on current telecom applications. He suggests that their method could be used to generate high-performance microwave signals that could be used in next-generation wireless communication networks, or used to improve transmissions between satellites.

The research work has been published by Applied Physics Letters in its August 22, 2005 issue under the name “Optically controlled slow and fast light in optical fibers using stimulated Brillouin scattering” (Volume 87, Issue 8, Article 081113). Here is a link to the abstract which is reproduced below for your convenience.

We demonstrate a method to achieve an extremely wide and flexible external control of the group velocity of signals as they propagate along an optical fiber. This control is achieved by means of the gain and loss mechanisms of stimulated Brillouin scattering in the fiber itself.

Our experiments show that group velocities below 71 000 km/s on one hand, well exceeding the speed of light in vacuum on the other hand and even negative group velocities can readily be obtained with a simple benchtop experimental setup. We believe that the fact that slow and fast light can be achieved in a standard single-mode fiber, in normal environmental conditions and using off-the-shelf instrumentation, is very promising for a future use in real applications.

In this abstract, as in the news release, the researchers give a number for “group velocities” slower than c, but not a single one for those faster than c. I wonder why…

Update (August 22, 2005): Here are Luc Thévenaz’s comments in reaction to the above note, which he nicely allowed me to reproduce.

Most of your comments are right, just be aware that what is really important for applications is delaying and advancing a signal, not the real speed of propagation. This makes possible a synchronisation of optical signals, that was impossible to realize so far with a control by light.

You look very suspicious about our capability to propagate faster than the speed of light in vacuum and you wonder why we mentioned no figure about this. Hmmm, I think you were a bit lazy and you did not read entirely our APL article. The answer is in the 3 last paragraphs, read carefully. We state clearly that we could achieve an infinite and even negative group velocity! We even show a graph of our measurements. We also give explanations why this does not break the principles of relativity and causality in the next paragraph and information still propagates slowlier than the vacuum light velocity.

I just want to mention that what we have just reported experimentally was already predicted theoretically and fully explained during the 1910s by Leon Brillouin and Arnold Sommerfeld. Nothing new and no paradox, there is nothing magic behind and no theory needs to be revisited.

Finally, Luc sent me a copy of the full APL paper. Here is a link to this paper (PDF format, 3 pages, 75 KB).

Sources: EPFL news release, August 19, 2005; and various web sites

Related stories can be found in the following categories.

• Future
  
  
• Optics
  
  
• Photonics
  
  
• Physics
  

And remember that comments are no longer accepted here because of a vandal. If you want to tell me something about this post, please go to the bottom right of this page and send me an e-mail.

This story could come from the imagination of a screenwriter working on the next James Bond movie, but it’s reality. Japanese physicists have found a way to store data inside your fingernails by using lasers. And, more importantly, they were able to read this data by using an optical microscope. Technology Research News reports that storing data in our fingernails could lead to new ways of authentication. Of course, data is only available for six months. After that the fingernail has grown and the data has disappeared. Still, the researchers think that such a method could have some practical implementations within three years.

Here is the opening of the article.

Researchers from the University of Tokushima and Hokkaido University have demonstrated that it is possible to read data written into a human fingernail using a laser, much like information is written on a rewritable compact disc. The data is read using an optical microscope.

And how does this method work?

[The researchers] wrote dot patterns into a fingernail using a laser that emitted pulses lasting a few million billionths of a second. The molecules of the fingernail that were hit by the laser became ionized, and because ionized molecules repulse each other, they caused a tiny explosion. The explosion changed the structure of the material at that location by decomposing the keratin protein molecules located there. These areas can be read because they fluoresce, or absorb and emit light, at a higher rate than the surrounding fingernail material.

And how much data can they store?

Two gigabits of data can be written per cubic centimeter of fingernail using these size dots. Today’s compact discs hold about 5.6 gigabits of data. A practical fingernail recording area of 5 millimeters by 5 millimeters by one tenth of a millimeter deep would hold 5 megabits of data, or about 300 pages of text.

Of course, this data is secure, at least for the duration of the life of your fingernails.

The researchers’ proof-of-concept samples could still be read 172 days after recording. This is probably the practical limit of fingernail storage because after six months a fingernail has grown enough to be completely replaced.

Will this method for carrying personal data will really be used within three years as are thinking the researchers? I’m not sure.

If you want to learn more about this technology, the latest research work has been published by Optics Express in June 2005 under the title “Three-dimensional optical memory using a human fingernail” (Vol. 13, No. 12, Pages 4560 - 4567, June 13, 2005). Here are two links to the abstract and to the full paper (PDF format, 8 pages, 1.11 MB).

And here are two links to previous papers from 2004 about the same subject, “Optical Bit Recording in a Human Fingernail” and “Processing Structures on Human Fingernail Surfaces Using a Focused Near-Infrared Femtosecond Laser Pulse.”

Sources: Kimberly Patch, Technology Research News, July 27/August 3, 2005; and various web sites

Related stories can be found in the following categories.

• Optics
  
  
• Photonics
  
  
• Physics
  
  
• Security
  
  
• Storage
  

And remember that comments are no longer accepted here because of a vandal. If you want to tell me something about this post, please go to the bottom right of this page and send me an e-mail.

Laser lights can be used for optical sensing applications, for example to identify unknown gases emitted by an engine. And as these unknown substances react differently to different wavelengths, researchers at the University of Wisconsin at Madison have developed unique wavelength-agile lasers. And I’m amazed by the beauty and the simplicity of their idea. They’re using white lasers which produce all colors simultaneously — but with a twist. The white laser light goes through a 20-kilometers long optical fiber before reaching its target. And because different colors ‘travel’ at different speeds, this produces independent results for the different wavelengths. The researchers are using spectral resolutions smaller than a thousandth of a nanometer and they are able to get all the results within a millionth of a second. This method could be used to design cleaner engines or data storage applications in a few years. Read More…

Let’s start with some technical explanations about this technology developed by Professor Scott Sanders in his labs.

Sanders’ laser builds on a phenomenon known as supercontinuum generation, in which researchers convert single-color lasers, such as a green or a red laser, into a multicolored beam using a special kind of optical fiber. Photonic crystal fibers enable them to generate this “white” laser beam, says Sanders.

While that method produces a range of laser colors-and thus, a large amount of information-the drawback is that the white laser delivers all of the colors simultaneously, says Sanders. Rather, researchers want to measure rapidly their subjects’ responses to individual colors.

So by directing the laser through an additional optical fiber about 20 kilometers long, Sanders created what he calls a “color-dependent speed limit.” Although all of colors leave the white laser at the same time, red travels through the fiber more quickly, while blue brings up the rear, and the rest of the colors fall somewhere in the middle. In photographs, they look like a continuous stream; in reality, each color exits the long fiber one after the other, like drops from a faucet. The entire laser scan occurs in a couple of millionths of a second.

Below is a photo showing how UW-Madison engine researchers gather useful data about the gases they study by using these wavelength agile lasers (Credit: UW-Madison College of Engineering).

Here is a link to a higher quality of this picture (3,264 x 2,448 pixels, 5.04 MB).

This research work about ‘rainbow’ lasers is making the cover story of Optics and Photonics News in its May 2005 issue. Full access to the paper (PDF format, 6 pages, 446 KB) is available via this page about “Wavelength-Agile Lasers.”

The figure below, which shows the evolution of wavelength-agile lasers within the author’s laboratory, has been extracted from this article (Credits: UW-Madison College of Engineering and Optics and Photonics News).

These colorful lasers should soon be used in such applications as spectroscopy or high-speed scanning.

Sources: University of Wisconsin at Madison, April 28, 2005; and various websites

Related stories can be found in the following categories.

• Engineering
  
  
• Nanotechnology
  
  
• Optics
  
  
• Photonics
  
  
• Sensors